Unusual photoluminescence of porous CdS (CdSe) crystals.

Low temperature photoluminescence (PL) is used to study photoetched (PE) CdS (CdSe). This surface treatment produces a porous fractal-type morphology, with superior photovoltaic properties. While most of the usual features in the PL spectrum are suppressed after PE, a new broad spectral band is observed which is deeper than the original bound exciton (I2) line. In contrast with previously known centers, this band shows remarkably large shift as a function of light intensity, which can be described by scaling laws. A theoretical model is proposed, which considers the excitonic emission in porous media. According to this model, the coulombic energy of the exciton increases due to the reduced polarizability of the composite media. Good agreement is obtained between theory and experimental data, and self-consistency is established for the parameters of the theory.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30024/1/0000392.pd

Discontinuity of capacitance at the onset of surface superconductivity

The effect of the magnetic field on a capacitor with a superconducting electrode is studied within the Ginzburg-Landau approach. It is shown that the capacitance has a discontinuity at the onset of the surface superconductivity $B_{\rm c3}$ which is expressed as a discontinuity in the penetration depth of the electric field into metals. Estimates show that this discontinuity is observable with recent bridges for both conventional and high-$T_{\rm c}$ superconductors of the type-II

Protein folding using contact maps

We present the development of the idea to use dynamics in the space of contact maps as a computational approach to the protein folding problem. We first introduce two important technical ingredients, the reconstruction of a three dimensional conformation from a contact map and the Monte Carlo dynamics in contact map space. We then discuss two approximations to the free energy of the contact maps and a method to derive energy parameters based on perceptron learning. Finally we present results, first for predictions based on threading and then for energy minimization of crambin and of a set of 6 immunoglobulins. The main result is that we proved that the two simple approximations we studied for the free energy are not suitable for protein folding. Perspectives are discussed in the last section.Comment: 29 pages, 10 figure

The type numbers of closed geodesics

A short survey on the type numbers of closed geodesics, on applications of the Morse theory to proving the existence of closed geodesics and on the recent progress in applying variational methods to the periodic problem for Finsler and magnetic geodesicsComment: 29 pages, an appendix to the Russian translation of "The calculus of variations in the large" by M. Mors

Discrete approaches to quantum gravity in four dimensions

The construction of a consistent theory of quantum gravity is a problem in theoretical physics that has so far defied all attempts at resolution. One ansatz to try to obtain a non-trivial quantum theory proceeds via a discretization of space-time and the Einstein action. I review here three major areas of research: gauge-theoretic approaches, both in a path-integral and a Hamiltonian formulation, quantum Regge calculus, and the method of dynamical triangulations, confining attention to work that is strictly four-dimensional, strictly discrete, and strictly quantum in nature.Comment: 33 pages, invited contribution to Living Reviews in Relativity; the author welcomes any comments and suggestion